25 
Part VI.] Preparation of Turpentine , Rosin and Gum. 
the form of a well-churned emulsion. This emulsion offers many diffi¬ 
culties in subsequent separation, as the emulsion when evaporated 
becomes dark brown on exposure, due to the salts of tannin extracted 
from the woody chips and pieces of bark contained in the crude material.. 
It 13 practically impossible to recover the gum in its original purity of 
colour and texture, unless it is treated in porcelain or enamelled ware 
and dried by a vacuum process, which is too costly to be adopted for the 
recovery of such a cheap material and even then the colour of the 
gum cannot be brought up to the natural hue. Again, the gum forms- 
a coating over the resin which being impermeable to the usual solvents 
cannot be extracted with the help of any well-known solvent as easily- 
as it is possible to do so in its original state. 
It was, however, observed that by passing superheated steam over 
the crude material placed in a steam jacketed still, it was possible to 
distil the oil out without causing any injury to the texture of the gum, 
but by doing so the resin becomes fused by the superheated steam, run& 
out and sticks to the still, and can only be recovered with the help of a 
solvent. From what has been said above, the solution to the problem 
of separating the three products one from another resolves itself into 
either solvent extraction followed by steam distillation or steam distilla¬ 
tion followed by solvent extraction. 
2. Solvents. 
Before discussing the process adopted, it is necessary to consider, 
from a commercial point of view, the different solvents suitable for the 
extraction of the Boswellia resin. It has not been possible to try all 
the different solvents on a-large scale, but as all of them have similar 
boiling points, any one of them may prove suitable according to the local 
conditions of work from the standpoint of comparative cost, loss during 
recovery and inflammability. It must be borne in mind that it has not 
been possible to determine the loss of solvent during recovery for want 
of proper plant at the Forest Research Institute, this being a very 
important point and for the same reason it has not been possible 
to try all the different solvents which may be suitable when working 
on a commercial scale. All that it has been possible to do is to carry 
out actual experiments on a Jarge scale in the Institute distillery 
with only two solvents, viz., petroleum benzine (boiling point up to 
80°C) and alcohol. As regards the recovery, though it was not possible 
to work out figures at the Institute, the data available as to the loss of 
solvent during the extraction of fixed oils and fats from oil-seeds in 
factories working these products has been ascertained, and may be taken 
to represent a fair average figure. The modern extraction plant is so 
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